Solid-state lighting modules, such as LED lighting modules, may have strict specifications as regards e.g. high light flux (e.g. >10,000 lm), high power efficiency (e.g. >120 lm/W), low cost, high electrical insulation (e.g. >2 kV AC) and high reliability (e.g. only 5% of LED modules may experience a failure after 100,000 working hours).
It has been ascertained that an important factor in causing failures consists of failures in solder joints, e.g. when high-power LEDs with ceramic package are soldered onto Insulated Metal Substrate (IMS) boards, especially when the base metal is aluminium.
One of the factors which may play a role in causing failures consists of thermo-mechanical stresses, such as the strain induced during thermal cycles by a mismatch in the CTEs (Coefficient of Thermal Expansion) of the component (e.g. the LED), the solder joints and the mounting board, e.g. the Printed Circuit Board (PCB).
It has been observed that a way to improve the reliability of solder joints, e.g. for LED components, may involve the use of IMS boards with a base metal such as copper, having a low CTE, and/or the use of dielectric materials with a low Young's modulus. These solutions, however, may involve various drawbacks regarding cost increase, galvanic corrosion and reduced reliability of the electrical insulation.
It has moreover been observed that it is possible to employ, instead of IMS boards, FR4 or ceramic boards. The former solution involves a lower thermal dissipation than IMS boards. The second solution has rather high costs and exhibits a large sensitivity to vibrations.
Still another solution may be the use of components (e.g. LEDs) with a plastic package. This however leads to a strong reduction in the performances (specifically in output light flux and efficiency) due to the higher thermal resistance of plastic packages in comparison with ceramic packages.